This invention relates generally to devices and methods for performing cardiovascular, pulmonary and neurosurgical procedures wherein the patient is placed on cardiopulmonary bypass. More specifically, the invention relates to devices and methods for venting blood and other fluids from the heart while the heart is under cardioplegic arrest and the patient is on cardiopulmonary bypass.
Various cardiovascular, neurosurgical, pulmonary and other interventional procedures, including repair or replacement of aortic, mitral and other heart valves, repair of septal defects, pulmonary thrombectomy, coronary artery bypass grafting, treatment of aneurysms, and neurovascular procedures, may require general anesthesia, cardiopulmonary bypass, and arrest of cardiac function. In order to arrest cardiac function, the heart and coronary blood vessels must be isolated from the remainder of the circulatory system. Using current techniques, isolation of the heart and coronary blood vessels is accomplished by placing a mechanical cross-clamp externally on the ascending aorta downstream of the ostia of the coronary arteries, but upstream of the brachiocephalic artery. A catheter is then inserted directly into the ascending aorta between the cross-clamp and the aortic valve, and cardioplegic fluid is infused through the catheter into the ascending aorta from which it flows into the coronary arteries to perfuse the myocardium. An additional catheter may be introduced into the coronary sinus for retrograde perfusion of the myocardium with cardioplegic fluid. In addition, the myocardium is usually cooled by irrigating with cold saline solution and/or application of ice or cold packs to the heart. Cardiac contractions will then cease.
While the heart is stopped, circulation is maintained throughout the body by a cardiopulmonary bypass system. A venous cannula is placed in a major vein such as the inferior vena cava in order to withdraw deoxygenated blood from the body. The deoxygenated blood is directed to a blood oxygenator which restores the blood with oxygen, and the oxygenated blood is pumped back into a major artery downstream of the aortic cross-clamp through an arterial return cannula.
Although the patient is on cardiopulmonary bypass, a certain amount of blood not withdrawn through the venous cannula returns through the venous system to the heart. In addition, cardioplegic fluid delivered into the coronary arteries drains back into the heart through the coronary sinus. Therefore, the heart must be vented to prevent an excessive quantity of blood and other fluids from pooling in the heart while it is not beating. To accomplish this, a venting cannula may be introduced through the aortic wall into the aorta upstream of the cross-clamp to withdraw fluid from the aortic root. Alternatively, a venting cannula may be introduced through a wall of the pulmonary artery near the point at which it connects to the right ventricle of the heart to allow blood to be withdrawn from the pulmonary artery. In procedures in which the heart itself is surgically opened, a venting cannula may be introduced directly into the heart through the incision in the heart wall.
Known techniques for performing major surgeries such as coronary artery bypass grafting and heart valve repair and replacement have generally required open access to the thoracic cavity through a large open wound, known as a thoracotomy. Typically, the sternum is cut longitudinally (a median sternotomy), providing access between opposing halves of the anterior portion of the rib cage to the heart and other thoracic vessels and organs. An alternate method of entering the chest is via a lateral thoracotomy, in which an incision, typically 10 cm to 20 cm in length, is made between two ribs. A portion of one or more ribs may be permanently removed to optimize access.
In procedures requiring a median sternotomy or other type of thoracotomy, the ascending aorta is readily accessible for placement of an external cross-clamp, and for introduction of a cardioplegic fluid delivery cannula and venting cannula through the aortic wall. The pulmonary artery is exposed as well to allow introduction of a venting catheter through the pulmonary arterial wall. However, such surgery often entails weeks of hospitalization and months of recuperation time, in addition to the pain and trauma suffered by the patient. Moreover, while the average mortality rate associated with this type of procedure is about two to fifteen per cent for first-time surgery, mortality and morbidity are significantly increased for reoperation. Further, significant complications may result from such procedures. For example, application of an external cross-clamp to a calcified or atheromatous aorta may cause the of release of emboli into the brachiocephalic, carotid or subclavian arteries with serious consequences such as strokes.
Methods and devices are therefore needed for isolating the heart and coronary arteries from the remainder of the arterial system, arresting cardiac function, venting the heart, and establishing cardiopulmonary bypass without the open-chest access provided by a median sternotomy or other type of thoracotomy. In particular, methods and devices are needed which facilitate venting the heart sufficiently to allow the heart to be placed under cardioplegic arrest with full cardiopulmonary bypass, without requiring open-chest access to the heart and without requiring an incision or puncture in the aorta, in the pulmonary artery, or in the heart wall.
The descriptive terms downstream and upstream, when used herein in relation to the patient""s vasculature, refer to the direction of blood flow and the direction opposite that of blood flow, respectively. In the arterial system, downstream refers to the direction further from the heart, while upstream refers to the direction closer to the heart, with the opposite true in the venous system. The terms proximal and distal, when used herein in relation to instruments used in the procedure, refer to directions closer to and farther away from the operator performing the procedure.
The present invention is directed to an endovascular approach for preparing a patient""s heart for cardiac procedures which does not require a grossly invasive thoracotomy. The invention facilitates venting fluids from a patient""s heart while the heart is placed under cardioplegic arrest and circulation is maintained by a cardiopulmonary bypass system without necessitating a median sternotomy or other thoracic incision and without requiring punctures or incisions in the heart, aorta, pulmonary artery, or other vessels.
In a first aspect of the invention, a venting catheter is provided for withdrawing blood from a pulmonary artery connected to a right ventricle of a patient""s heart. The venting catheter comprises a flexible elongate shaft having a distal end, a proximal end, and an inner lumen extending from the proximal end to an inlet port at the distal end. Usually, a plurality of inlet ports are provided at the distal end in communication with the inner lumen. The shaft has a length selected to allow the distal end to be positioned in the pulmonary artery with the proximal end extending transluminally to a peripheral vein and out of the patient through a puncture in the peripheral vein. Usually, the shaft is at least about 40 cm in length to allow the venting catheter to be introduced into the internal jugular vein in the neck and advanced into the pulmonary artery via the superior vena cava. The inner lumen is configured to allow blood to be withdrawn from the pulmonary artery at a rate of at least 50 ml/min. at a pressure no lower than xe2x88x92350 mmHg. In a specific embodiment, the inner lumen has cross-sectional area of at least 4.0 mm2.
In a preferred embodiment, the venting catheter may include an expandable member mounted to the shaft near the distal end. The expandable member may serve several purposes. The expandable member may be configured to be carried by blood flow through the heart into the pulmonary artery. In addition, the expandable member may be configured to occlude the pulmonary artery when expanded. Usually, the expandable member comprises a balloon, and the shaft has an inflation lumen extending from the proximal end to an opening near the distal end in communication with the interior of the balloon. Alternatively, the expandable member comprises an expandable frame to which a flow resistant membrane is mounted. The expandable frame may include a plurality of flexible beams mounted longitudinally to the shaft and configured to deflect outwardly when under compression. The flow-resistant membrane may comprise an elastomeric web between the flexible beams.
The venting catheter may also include means for measuring pressure in the pulmonary artery. The pressure measurement means may comprise a pressure lumen extending through the shaft from the proximal end to a pressure port near the distal end.
The shaft of the venting catheter may have a proximal portion which defines a longitudinal axis, and a distal portion which is disposed at an angle of less than about 120xc2x0, and usually less than about 90xc2x0, relative to the longitudinal axis. This facilitates placement of the distal end in the pulmonary artery when introducing the catheter transluminally from a peripheral vein into the heart. In a preferred embodiment, the distal portion is disposed at an angle about 50xc2x0-60xc2x0 relative to the proximal portion, facilitating placement of the distal end in the pulmonary artery when the venting catheter is introduced into the heart via the superior vena cava.
The venting catheter may be used as part of a system for venting blood from the heart during cardiac procedures involving cardiopulmonary bypass. In addition to the venting catheter, such a system according to the invention includes flow-directed means for guiding the distal end of the shaft into the pulmonary artery from the right ventricle, and pump means in communication with inner lumen at the proximal end of the shaft for withdrawing blood from the pulmonary artery through the inner lumen at a rate of at least 50 m/min at a pressure no lower than xe2x88x92350 mmHg.
The flow-directed means may comprise either an integral part of the venting catheter itself, or a separate device. In one embodiment, the flow-directed means comprises an expandable member mounted near the distal end of the venting catheter which floats with blood flow through the right side of the heart into the pulmonary artery. Alternatively, the flow-directed means may be a separate flow directed catheter such as a Swan-Ganz catheter or wedge pressure catheter which has a small-diameter flexible shaft with a balloon mounted to its distal end. The flow-directed catheter is first positioned in the inner lumen of the venting catheter and advanced so that the distal end of the flow-directed catheter is distal to the venting catheter. The flow-directed catheter is then introduced into a peripheral vein such as an internal jugular vein, advanced into the right atrium, and its balloon then inflated. The inflated balloon will be guided into the right ventricle and into the pulmonary artery by the flow of blood through the heart. The venting catheter is then slidably advanced over the flow-directed catheter until the distal end is positioned in the pulmonary artery. The flow-directed catheter is then removed from the patient.
The pump means of the system may comprise any of various types of blood pumps utilized in medical procedures. For example, the pump may be a centrifugal pump or roller pump of the type utilized in cardiopulmonary bypass systems. In a preferred embodiment, the pump means is part of a cardiopulmonary bypass system configured to receive blood from the inner lumen of the venting catheter as well as deoxygenated blood withdrawn from the venous system of the patient, oxygenate the blood, and return the blood to an artery in the patient. The cardiopulmonary bypass system is preferably configured for connection to peripheral vessels in the patient, and includes a venous cannula suitable for introduction in a peripheral vein such as a femoral vein, and an arterial return cannula suitable for introduction in a peripheral artery such as a femoral artery.
In order to facilitate inducing cardioplegic arrest, the system of the invention may further include means for arresting the patient""s heart. The means for arresting the heart preferably includes means for occluding the lumen of the patient""s aorta between the coronary ostia and the brachiocephalic artery. In a particular embodiment, the occlusion means comprises an aortic catheter introduced through a peripheral artery into the aorta. The aortic catheter has a balloon on its distal end which, when expanded, occludes the aortic lumen. The aortic catheter also includes an inner lumen which opens at a port distal to the balloon to allow a cardioplegic fluid such as cold aqueous potassium chloride mixed with blood to be delivered through the inner lumen into the aortic root, from which the fluid flows into the coronary arteries. By isolating the coronary arteries from the arterial system and delivering cardioplegic fluid, heart contractions will quickly cease, with the patient""s circulation maintained by the cardiopulmonary bypass system. While the heart is stopped, blood and other fluids are withdrawn from within the heart by the venting catheter positioned in the pulmonary artery.
In a further aspect of the invention, a method of venting blood from a patient""s heart comprises the steps of:
introducing a venting catheter into a peripheral vein;
advancing the venting catheter through the peripheral vein and into a right ventricle of the patient""s heart;
positioning a distal end of the venting catheter in a pulmonary artery leading away from the right ventricle; and
withdrawing blood from the pulmonary artery through an inner lumen in the venting catheter.
Usually, the peripheral vein into which the venting catheter is introduced comprises the internal jugular vein which can be accessed percutaneously or by surgical cut-down in the patient""s neck. Alternatively, the peripheral vein could be a right subclavian vein, also in the patient""s neck, a femoral vein, accessible in the patient""s groin, or other peripheral vein of suitable size and location to allow the venting catheter to be positioned intraluminally and advanced into the heart via the inferior vena cava or superior vena cava.
In a preferred embodiment, blood is withdrawn from the pulmonary artery at a rate of at least 50 ml/min at a pressure no lower than xe2x88x92350 mmHg. This facilitates venting the heart at a sufficient rate to keep excessive quantities of blood from pooling in the heart, while keeping pressure at a level which will not cause undue hemolysis.
In one embodiment, the step of positioning comprises introducing a flow-directed catheter into the peripheral vein before the step of introducing the venting catheter. The flow-directed catheter is advanced through the peripheral vein and into the patient""s heart. An expandable member on the distal end of the flow-directed catheter is then expanded so that the expanded flow directed catheter is carried by blood flow through the heart into the pulmonary artery. The flow-directed catheter is positioned in the inner lumen of the venting catheter, and the venting catheter is slidably advanced over the flow-directed catheter into the pulmonary artery. In an alternative embodiment, the step of positioning comprises expanding an expandable member on the distal end of the venting catheter, the expanded expandable member being carried by blood flow through the heart into the pulmonary artery.
The method may further include a step of measuring pressure in the pulmonary artery through a pressure lumen in the venting catheter or by other pressure measurement means at the distal end of the venting catheter.
In addition, the pulmonary artery may be occluded by an occluding member on the distal end of the venting catheter while withdrawing blood therefrom.
The method will usually include a step of arresting the heart, wherein the coronary arteries are isolated from the remainder of the arterial system, and a cardioplegic fluid is delivered into the coronary arteries to perfuse the myocardium to arrest cardiac function. Preferably, this is accomplished by means of the above-described aortic occlusion catheter. When the heart is stopped, circulation is maintained by a cardiopulmonary bypass system which removes deoxygenated blood from a peripheral vein in the patient, oxygenates the withdrawn blood, and returns the oxygenated blood to a peripheral artery in the patient.
Using the system and method of the invention, a patient""s heart can be arrested and the patient placed on cardiopulmonary bypass without a thoracotomy, thereby reducing mortality and morbidity, decreasing patient suffering, reducing hospitalization and recovery time, and lowering medical costs relative to previous open-chest procedures. The venting catheter of the invention facilitates venting of blood and other fluids from the heart while the heart is under cardioplegic arrest and the patient is supported on cardiopulmonary bypass, without need for a open-chest access and without need for a puncture or incision in the aorta, in the pulmonary artery, or in the heart itself.
With the venting catheter in place, the heart arrested and cardiopulmonary bypass established, the patient is prepared for a variety of surgical and diagnostic procedures, including repair or replacement of aortic, mitral and other heart valves, repair of septal defects, pulmonary thrombectomy, coronary artery bypass grafting, angioplasty, atherectomy, electrophysiological mapping and ablation, treatment of aneurysms, transmyocardial revascularization, as well as neurovascular and neurosurgical procedures. While such procedures may be performed through a thoracotomy in the conventional manner, the invention provides the capability for performing procedures such as heart valve replacement or coronary artery bypass grafting using minimally-invasive techniques, either by means of surgical instruments introduced endovascularly through an artery or vein, or by means of thoracoscopic instruments introduced through small incisions in the chest wall.
Moreover, as mentioned, the system may even be employed in conventional open-heart procedures. These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.